Maybe the part where there were still a lot of people even in 1991 that wanted to stay?
(Yes, there were also independence referendums in 1991, but you were asking why it didn’t happen earlier.)
Source: https://www.sudd.ch/event.php?lang=en&id=su011991
I was asking why it didn’t happen earlier because before the Union those countries were “We don’t want to be in the union” and after the union those countries were “We said, we didn’t want to be in the union”. If before the union they didn’t want to be in it and after the union they still said they didn’t want to be in it then why should we assume that during the union they wanted to be in it? The answer is that they didn’t, they simply weren’t allowed to leave.
We said
Who is we? The bourgeoisie or the proletariat? There’s going to be severe conflicts of interest here.